FIG. 1 is a schematic representation of a common light guide design shown in side view 10 and in bottom view 11. Typically, the light source used in this case is cold cathode fluorescent lamp (CCFL) 100, placed at one edge of a plastic (for example acrylic) light guide 101. Light from light source 100 is incident into light guide 101 and is transmitted along light guide 101 through successive specular internal reflections. In order for light to exit from top surface 105, dots 103 are patterned on bottom surface 106 of light guide 101. When light is incident on a dot, for example dot 103, it is reflected in a diffuse manner and is then refracted out through top surface 105. To prevent light loss through bottom surface 106, white reflector layer 104 is applied to bottom surface 106. Similarly, to ensure that top surface 105 has luminance uniformity, diffuse translucent film 102 is applied to top layer 105.
The amount of light that is directed toward top surface 105 and the uniformity of luminance of top surface 105 are dependent on the pattern of dots 103 on bottom surface 106. An important parameter is the surface area of the dot, i.e., the dot size. A common design comprises a series of small dots near light source 100 that gradually increase in area proportionally with distance from light source 100. Therefore, the gradient of increase in surface area of the dots is in the x-direction shown by the coordinate axis in FIG. 1. As the light gets weaker, due to prior reflections as it propagates down light guide 101, the dot size is increased to ensure that the amount of light reflected from the dots still remains substantially the same. The dot pattern is thus configured such that the amount of light reflected from the dots is substantially the same along every incremental distance in the x-direction.
The dot pattern illustrated in FIG. 1 is particularly suitable for a light source such as a CCFL, in which light is emitted from all sides with fairly uniform intensity, i.e., omni-directional light intensity. FIG. 2 is a graphical representation showing the uniformity of the light, for example, in the x-direction. In this illustration, the lengths of arrows 200, which represent intensities in the x-direction, are generally uniform. As such, the design of the dot pattern is fairly straightforward. The dot area in the pattern has a uniformly increasing gradient from the end where the light source is located to the other extreme end.